as.numeric with comma decimal separators?

问题

I have a large vector of strings of the form:

Input = c("1,223", "12,232", "23,0")

etc. That's to say, decimals separated by commas, instead of periods. I want to convert this vector into a numeric vector. Unfortunately, as.numeric(Input) just outputs NA.

My first instinct would be to go to strsplit, but it seems to me that this will likely be very slow. Does anyone have any idea of a faster option?

There's an existing question that suggests read.csv2, but the strings in question are not directly read in that way.

回答1:

as.numeric(sub(",", ".", Input, fixed = TRUE))

should work.

回答2:

scan(text=Input, dec=",")
## [1]  1.223 12.232 23.000

But it depends on how long your vector is. I used rep(Input, 1e6) to make a long vector and my machine just hangs. 1e4 is fine, though. @adibender's solution is much faster. If we run on 1e4, a lot faster:

Unit: milliseconds
         expr        min         lq     median         uq        max neval
  adibender()   6.777888   6.998243   7.119136   7.198374   8.149826   100
 sebastianc() 504.987879 507.464611 508.757161 510.732661 517.422254   100

回答3:

Also, if you are reading in the raw data, the read.table and all the associated functions have a dec argument. eg:

read.table("file.txt", dec=",")

When all else fails, gsub and sub are your friends.

回答4:

Building on @adibender solution:

input = '23,67'
as.numeric(gsub(
                # ONLY for strings containing numerics, comma, numerics
                "^([0-9]+),([0-9]+)$", 
                # Substitute by the first part, dot, second part
                "\\1.\\2", 
                input
                ))

I guess that is a safer match...

回答5:

The readr package has a function to parse numbers from strings. You can set many options via the locale argument.

For comma as decimal separator you can write:

readr::parse_number(Input, locale = readr::locale(decimal_mark = ","))

回答6:

As stated by , it's way easier to do this while importing a file. Thw recently released reads package has a very useful features, locale, well explained here, that allows the user to import numbers with comma decimal mark using locale = locale(decimal_mark = ",") as argument.

回答7:

The answer by adibender does not work when there are multiple commas.

In that case the suggestion from use554546 and answer from Deena can be used.

Input = c("1,223,765", "122,325,000", "23,054")
as.numeric(gsub("," ,"", Input))

ouput:

[1] 1223765 122325000 23054

The function gsub replaces all occurances. The function sub replaces only the first.

来源：https://stackoverflow.com/questions/15236440/as-numeric-with-comma-decimal-separators

标签

string

number-formatting